1. Field of the Invention
The present invention relates to a position-to-digital encoder for generating binary coded electric signals in accordance with the relative positions between a brush member and a series of contacts arranged in order. The combination of the brush member and a series of contacts may be replaced by a combination of a light emitting member and a series of light sensitive elements. Thus, it is to be understood that although reference is made to the brush member and the series of contacts for the convenience of describing the invention, such terminology includes the above replacement. The digital encoder according to the present invention is suitable, although not exclusively, for use in camera exposure control circuitry which determines, or electrically sets, a binary coded signal to represent a set exposure factor or the position of an exposure setting member for a camera.
2. Prior Art
Apparatus are known or have been proposed which control the exposure time, diaphragm aperture or both, of cameras utilizing digital signals in the form of a binary code. Encoders employing a binary coded plate, as shown in FIG. 1, for obtaining binary coded signals representative of set exposure factors, such as film sensitivity or preset diaphragm aperture value, or the positions of an exposure setting member for an automatically controlled exposure factor, are known. The encoder of FIG. 1 includes code plate 1 with electrically conducting portions 1a (blackened positions in the Figure), brush plate 2 with a plurality of contacts 2a slidable over code plate 1 in the directions of the arrows, and electrical lines leading from each contact. With that construction, signals appear at the lines connected to the respective contacts that are in contact with conducting portions 1a so that binary coded signals are obtained through the lines in accordance with the position of brush plate 2 relative to code plate 1. The movement of brush plate 2 is associated with, for example, the setting of an exposure factor, so that the binary coded signal represents the set exposure factor.
However, the above construction has disadvantages, especially when it is used for cameras. In general the elements of a camera are required to be as small as possible. However, the above mentioned encoder has a limit with respect to a reduction of its dimensions, because it must have a width for accomodating the number of bits corresponding to that of the contacts on brush plate 2, and a length accomodating the number of signals to be discriminated. In other words, the number of the segments, i.e. conducting and non-conducting portions on code plate 1 must be equal lengthwise to the number of the exposure factor settings and widthwise to the number of the binary coded digits.
In addition, the above structure is liable to provide incorrect information when the contacts are at a boundary between adjacent segments and in contact with two rows of the segments. For example, if the contacts are at the boundary between the rows of segments representing 3 and 4 respectively, and as the binary digits for 3 and 4 are 011 and 100, the contacts detect conducting portions in both rows to provide a signal of 111, i.e. 7 in the decimal system. This error is likely to occur more frequently with reduced dimensions and increases in the number of bits.